The present invention generally relates to display devices and more particularly to a light-emitting display device including a plasma display device or an EL (electro-luminescence) display device.
A plasma display device or an EL (electro-luminescence) display device is a flat display device of the light-emission type. One important application of such light-emitting flat display devices is televisions having a very large screen size.
FIG. 1 shows the construction of a plasma display panel 10 of a so-called AC-type PDP (plasma display panel).
Referring to FIG. 1, the plasma display panel 10 includes rear-side glass substrate 11 and a front-side glass substrate 15, wherein the rear-side glass substrate 11 carries thereon a number of addressing electrodes 12 of a Cr/Cu/Cr stacked structure in the form of parallel bands extending in a column direction. Further, a dielectric layer 13 of a low-melting glass is deposited on the substrate 11 so as to cover the addressing electrode 12, and a rib structure 14 also of a low-melting glass is formed on the dielectric layer 13 such that the rib structure 14 includes a number of ribs each extending in the column direction such that a pair of the ribs are disposed at both lateral sides of each of the addressing electrodes 12. In the groove thus formed between a pair of the ribs, there is formed a layer of fluorescent material for the three primary colors of red (R), green (G) or blue (B), wherein the grooves for red, green and blue constitute together a single pixel.
On the front-side glass substrate 15, more precisely on the bottom principal surface of the front-side glass substrate 15 (see FIG. 1), there are provided a number of display electrodes 16 of a transparent conductive material such as ITO (In2O3xc2x7SnO2) in the form of parallel bands, wherein each of the display electrodes 16 extends in a row direction, which is perpendicular to the column direction. Further, a bus electrode 17 of the Cr/Cu/Cr structure extends on each of the display electrodes with a width substantially smaller than a width of the display electrode 16, and there is formed a dielectric film 18 of a low-melting glass on the substrate 15 so as to cover the display electrodes 16 and the bus electrodes 17 thereon. Further, there is provided a protective film 19 of MgO on the dielectric film 18.
The glass substrate 11 and the glass substrate 15 having such a construction are assembled such that the ribs 14 on the glass substrate 11 face the protective film 19 on the glass substrate 15 as represented in FIG. 1, and an inert gas such as Ar is confined between the space formed between the substrate 11 and the substrate 15.
In operation, a drive voltage is applied between a selected addressing electrode 12 and a selected display electrode 17, and the plasma induced as a result of the drive voltage causes a light emission in the predetermined fluorescent layers.
Because of the active, light-emitting nature of the plasma display panel, a plasma display device that uses such a plasma display panel requires a power drive circuitry for driving the plasma display panel, wherein such a power drive circuitry of a plasma display panel consumes an electric power far larger than the electric power that is consumed by a drive circuit of a liquid crystal panel. The same applies true also in other active type flat display device such as the one that uses an ELP (electro-luminescent panel) for the display panel.
In such a light-emitting flat display device, it is required that the number of the addressing electrodes 12 and/or the displaying electrodes 16 has to be increased in order to improve the resolution of representation, while this means that it is necessary to provide the driver integrated circuit chips constituting the power drive circuitry along the peripheral part of the display device with an increased mounting density.
For example, it is necessary, in the case of designing a 42-inch full-color plasma display device that has a resolution of 850xc3x97480 pixels, to provide the addressing electrodes 12 in total of 2550 (=850xc3x973; 850 for each of R, G and B), in addition to the display electrodes 16 provided with the number of 480. Thus, when the drive circuitry is formed by using the integrated circuit chips each having 60 output terminals, it is necessary to arrange 40 or more integrated circuit chips side by side in the lateral direction or row direction of the display panel. The number of the required integrated circuit chips increases further when a higher resolution is desired.
In view of the foregoing, various constructions are proposed for achieving the desired dense arrangement of the driver integrated circuit chips.
FIGS. 2 and 3 respectively show conventional constructions 20 and 20A for mounting the driver integrated circuit chips, wherein those parts in FIGS. 2 and 3 corresponding to the parts described previously are designated by the same reference numerals and the description thereof will be omitted.
Referring to FIG. 2 showing the construction 20 known as COB (chip-on-board), a driver integrated circuit chip is mounted directly on a printed circuit board for electrical interconnection. Thereby, the integrated circuit chips can be mounted with an increased density as compared with the case of mounting the same chips in the form accommodated in a package.
Referring to FIG. 2, the conventional construction 20 includes a printed circuit board 23 behind the glass substrate 11 and a driver integrated circuit chip 21 mounted on the printed circuit board 23, wherein the printed circuit board 23 is connected electrically to the addressing electrodes 12 or the bus electrodes 17 on the glass substrate 11 or on the glass substrate 15 via a flat cable 22xe2x80x2.
In the construction 20 of FIG. 2, the driver integrated circuits can be mounted on the printed circuit board 23 with high density. On the other hand, the printed circuit board 23 has a poor thermal conductivity due to the material used therefor, and because of this, the construction 20 has a drawback of poor heat dissipation. Thus, in the construction 20, there is a problem in that not only the driver integrated circuit chip 21 but also the printed circuit board 23 itself experiences a severe temperature rise, while such a severe temperature rise of the printed circuit board 23 raises a question with regard to the reliability of the printed circuit 23 itself or with regard to the reliability of other driver integrated circuits held on the printed circuit board 23.
On the other hand, the construction 20A of FIG. 3 is known as COG (chip-on-glass), which is under investigation particularly with regard to the art of liquid crystal display device for a high density mounting of the driver integrated circuit chips with reduced thickness. In the field of the liquid crystal display devices, there are reports that the COG construction 20A is used in practice.
Referring to FIG. 3, it should be noted that the driver integrated circuit chip 21 is attached to the glass substrate 11, and the driver integrated circuit 21 thus mounted on the substrate 11 is connected to the addressing electrodes 12 or to the bus electrodes 17 via bonding wires 21a and a flat cable 22. In the illustrated example, the flat cable 22 carries a connector 22A at a tip end thereof, and the connector 22A is used to electrically connect the flat cable 22 to the printed circuit board 23 that is provided at the rear side of the substrate 11. The printed circuit board 23 may carry integrated circuit chips 24 and 25 containing therein various control circuits.
In the construction 20A of FIG. 3, it should be noted that the driver integrated circuit chips 21 are aligned on the glass substrate along the edge part thereof with a large mounting density. In such a structure of FIG. 3, the dissipation of heat from the driver integrated circuit chips 21 thus arranged on the glass substrate 11 becomes inevitably poor in view of the poor thermal conductivity of the glass substrate 11. Thus, there may occur a severe temperature rise in the driver integrated circuits 21, which may lead the integrated circuit 21 to malfunction or to be damaged. Further, the heat thus transferred to the glass substrate 11 or 15 may induce a distortion in the plasma display panel 10. In the worst case, the plasma display panel 10 may be damaged.
Accordingly, it is a general object of the present invention to provide a novel and useful light-emitting flat display device wherein the foregoing problems are eliminated.
Another and more specific object of the present invention is to provide a light-emitting flat display panel wherein the efficiency of heat dissipation is improved substantially.
Another object of the present invention is to provide a flat display device, comprising:
a display panel;
a driver integrated circuit chip provided adjacent to said display panel in electrical connection thereto; and
a heat sink provided adjacent to said display panel, said heat sink carrying thereon said driver integrated circuit chip.
According to the present invention, the problem of heat dissipation, which arises in the high-resolution flat display device in which the driver integrated circuit chips have to be mounted with large density, is successfully avoided by forming the driver integrated circuit chips on a heat sink block.